“Commute ran the red, kept going and ran into the UP train on the main.”
So, had the freight train even gotten to the switch for the siding yet?
I can see what you are describing, but a map of the Metrolink line would be more helpful.
I searched for it, and it doesn’t seem to be available.
The accident happened before the UP train had arrived at the switch for the siding. I think the cause will come down to engineer error, he was distracted, ran the red and was exceeding a speed that would have permitted him to stop short of the red.